Abstract:

Plasma vitamin B₁₂ concentrations of 16 elderly women were
measured using the growth response of the microorganism, Ochromonas
malhamensis. The method required major modifications which
are described in detail. All women had plasma concentrations of
vitamin B₁₂ above the normal minimum of 200 pg/ml despite the fact
that the diets of nine women failed to meet the RDA of 3 μg/day. The
mean dietary B₁₂ of 11 women who took no supplemental B₁₂ was
2.90 μg/day; their mean plasma concentration was 415 pg/ml. The
group of five women who took B₁₂ preparations had an average total
intake of 13.89 μg/day and a significantly higher plasma concentration
(628 pg/ml). Supplemental intakes of ascorbic acid in the range of
200-1100 mg/day had no destructive effect on vitamin B₁₂ in plasma.